I haven't been using sauermalz at all (just using the calcium chloride with distilled water). Looks like what I'm seeing above is that I can simply use the calcium chloride and distilled water only, and not have any issues.

Skipping the acid malt is imperative for this grist. The mash pH and resulting wort pH will be too low with the acid malt. With just the RO water, I suggest that you NOT add calcium chloride or gypsum to the mash water to help reduce the potential for too low a mash pH with this potentially acidic grist. I would reserve those minerals and add them directly to the kettle to help keep the RA of the mash water from falling too low and taking the mash pH with it. Adding the minerals after the mash reduces that effect.

I've brewed about 2-3 stouts so far (I'm sort of a novice) and both have had an astringent/tannin off flavor (as have all of my beers). I was guided to purchase some gypsum and calcium chloride and start brewing with distilled water (instead of the Poland Spring water I've been using) using calcium chloride added.

First off, in your post, what is "acid malt?"

Second, I've brewed stouts with Poland Spring water and have not added anything, and had the astringent/tannin taste. Are you saying that if I use distilled (without additives) I won't have that problem?

Acid malt is basically just a pale malt that has had some lactic acid sprayed on the outside. It's used mainly to lower the mash pH if you're brewing a lighter colored beer and/or you have very alkaline water. Some recipes also use it in higher amounts to add some lactic acid flavor to the beer. Edit: It's also just another name for sauermalz.

RA stands for residual alkalinity. During the mash some of the calcium and magnesium will react with phosphates in the malt to produce some hydrogen ions which lowers the alkalinity of the water (http://www.howtobrew.com/section3/chapter15-3.html). Residual alkalinity is essentially an attempt to predict how much alkalinity will be remaining in the water after this reaction takes place. If you don't measure the pH of the mash, then residual alkalinity gives you a rough ballpark estimate of what sort of water you should be shooting for so that your mash pH will be in an acceptable range, but figuring out the 'correct' range for your residual alkalinity is even more of a hand-wavey estimate based on predictions about how the types of grain you're using will effect mash pH (darker grains lower the pH more than light grains).

Anyway, the general idea behind the instructions in the primer are that you dilute with RO/distilled water so that you start with mineral/ion/chlorine free water. From there you add some calcium chloride since these are important for both yeast health and overall beer flavor. If you're brewing a pale beer, then the acid malt is used to ensure that the mash pH gets low enough for a good conversion. For darker beers this isn't needed since the dark malts in the recipe will lower the mash pH enough on their own to get good conversion.

How are you doing your sparging? Tannin extraction can come during the sparge from having too high of a pH or too high of a temperature in the sparge water.

Acid malt is basically just a pale malt that has had some lactic acid sprayed on the outside. It's used mainly to lower the mash pH if you're brewing a lighter colored beer and/or you have very alkaline water. Some recipes also use it in higher amounts to add some lactic acid flavor to the beer. Edit: It's also just another name for sauermalz.

RA stands for residual alkalinity. During the mash some of the calcium and magnesium will react with phosphates in the malt to produce some hydrogen ions which lowers the alkalinity of the water (http://www.howtobrew.com/section3/chapter15-3.html). Residual alkalinity is essentially an attempt to predict how much alkalinity will be remaining in the water after this reaction takes place. If you don't measure the pH of the mash, then residual alkalinity gives you a rough ballpark estimate of what sort of water you should be shooting for so that your mash pH will be in an acceptable range, but figuring out the 'correct' range for your residual alkalinity is even more of a hand-wavey estimate based on predictions about how the types of grain you're using will effect mash pH (darker grains lower the pH more than light grains).

Anyway, the general idea behind the instructions in the primer are that you dilute with RO/distilled water so that you start with mineral/ion/chlorine free water. From there you add some calcium chloride since these are important for both yeast health and overall beer flavor. If you're brewing a pale beer, then the acid malt is used to ensure that the mash pH gets low enough for a good conversion. For darker beers this isn't needed since the dark malts in the recipe will lower the mash pH enough on their own to get good conversion.

How are you doing your sparging? Tannin extraction can come during the sparge from having too high of a pH or too high of a temperature in the sparge water.

I'm doing AG BIAB 1-gallon batches. I make sure my mash isn't too thin so I'm heating some of my sparge water to 165 in another kettle and dunk sparging my bag after I mash out (around 165). I then add that wort to my kettle. I normally achieve about 75% efficiency.

So what sort of water/grain ratio are you using in your mash and how much water are you dunking in during the sparge? Also how long do you let the grains soak after you dunk them?

Basically the biggest factors for tannin extraction are temperature, pH, and time - as you increase each of these tannin extraction will increase. If the Poland Spring water you've been using was alkaline, then when you dunk your grains the pH could be rising enough to draw out tannins (especially if you let them soak for a long period of time). Using RO water will help since it can't buffer as much acid so the pH won't rise as much.

Hmm, looks like it can be all over the place. They list ranges for alkalinity from 12-200ppm and bicarbonate between 15-250ppm (http://www.nestle-watersna.com/pdf/PS_BWQR.pdf). Probably worth switching to RO water just to get some consistency between bottles....

Hmm, looks like it can be all over the place. They list ranges for alkalinity from 12-200ppm and bicarbonate between 15-250ppm (http://www.nestle-watersna.com/pdf/PS_BWQR.pdf). Probably worth switching to RO water just to get some consistency between bottles....

Huh, the two times I've checked the alkalinity it's been ~1 degree kH (~17.3 ppm as CaCO3). We probably get the water from the actual Poland Springs, though.